1. Field of the Invention
The present invention relates to a webbing retractor adapted for use in a seatbelt system for protecting an occupant in an emergency situation of a vehicle to retract an occupant restraining webbing therein, and more particularly to a webbing retractor in which a webbing tension due to a retracting force of a webbing takeup shaft is decreased.
2. Description of the Prior Art
In the webbing retractor adapted for use in the seatbelt system, the webbing is secured at its one end to the takeup shaft which is rotated by a biasing force of a spiral spring to retract the webbing in layers thereon.
The biasing force of the spiral spring is set at a predetermined value or more so as to retract the webbing reliably on the takeup shaft after the occupant releases the webbing from its restraining situation on the occupant. Accordingly, the webbing must be unwound with a relatively large power when it is fastened on the occupant, and the webbing gives a relatively large pressure to the occupant when the occupant is restrained by the webbing.
In a conventional art such a webbing retractor has been proposed that a motor is used instead of the spiral spring and a driving force thereof is transmitted to the takeup shaft so that the takeup shaft is rotated to retract the webbing thereon.
In the webbing retractor, however, there is such a problem that a control of the motor is complicated and in some cases when the webbing is retracted on to the takeup shaft by the motor in order to cancel a slack of the webbing restraining the occupant a small shock is given to the occupant, especially, his shoulder portion, which results in an unpleasant feeling to the occupant.
In the webbing retractor there is also, in some cases, such a problem that when a trouble occurs in a control system, an electric system or a motor body it is made possible to only unwind the webbing from the takeup shaft.